1. Field
The present invention relates to an optical disc apparatus and an optical disc recording and reproducing method. In particular, the invention relates to an optical disc apparatus and an optical disc recording and reproducing method in which data is recorded and reproduced on and from a multi-layered recording type optical disc.
2. Description of the Related Art
As recording type optical discs, there are commercially available, for example, DVD-R, DVD-RW, DVD-RAM, Blu-ray Disc (BD) and the like. In these recording type optical discs, it is well known that the quality of a reproduction signal depends on a laser power (a recoding power) or the like used upon recording. Therefore, there is generally performed such a processing that a test term is prepared within a predetermined time period such as immediately after an optical disc has been inserted into an optical disc apparatus and then data is tentatively written in a test recording area (also called PCA: Power Calibration Area) provided on the disc within the test term to obtain an optimum recording power. This processing is called OPC (Optimum Power Calibration).
In obtaining the optimum recording power, what should be used as an evaluation index is important. Although various evaluation indices have been conventionally proposed, a so-called asymmetry value β is now being widely used as the evaluation index.
The optimum recording power differs for different type of the optical disc used. Thus, on an optical disc of a certain type, a recording power which has been recommended in advance is recorded in its predetermined area so as to read this recommended recording power into an optical disc apparatus used when the optical disc is inserted into the apparatus.
In addition, there is now being widely used a method in which recommended recording powers for various types of the optical disc have been stored in an appropriate memory of an optical disc apparatus in the manufacturing course thereof so as to read out a recommended recording power corresponding to the type of the optical disc inserted into the apparatus from its memory.
The optimum recording power also differs in accordance with the characteristic of the optical disc apparatus used and the environmental condition such as the temperature or the like around the apparatus. Therefore, the optimum recording power cannot be determined simply from the recommended recording power for the optical disc concerned. Thus, test data is recorded in a test recording area while changing the recording power within a predetermined range, centering on the recommended recording power read out from the optical disc used or from the memory of the optical disc apparatus used. Then, the recorded test data is reproduced to determine a recording power with which an evaluation index is optimized as the optimum recording power.
JP-A 2006-164417 discloses, for a two-layered recording type optical disc, a technique for determining optimum recording powers for a first layer (a layer which is the closest to a light incident side) and a second layer situated on the inner side of the first layer of the optical disc. In this technique, a correlation characteristic between an asymmetry value β for the first layer and an asymmetry value β for the second layer is stored as a β characteristic. A recording depth of an area of the first layer which physically constitutes a layer ahead of an area to be subjected to the OPC of the second layer is made uniform, a recording power for the second layer is acquired from a power characteristic corresponding to this recording depth of the first layer and the OPC is performed by the recording power thus acquired, thereby to acquire the optimum recording power for the second layer.
However, the overshoot amount of recording pulses, distribution of light quantity thereof, the spot form of a laser beam to be irradiated and the like change in accordance with a change in environmental condition such as the temperature or the like. Therefore, by the technique disclosed in JP-A 2006-164417, the above mentioned correlation characteristic (the β characteristic) changes accordingly. That is, the recording power for the second layer acquired from the β characteristic between the first and second layers deviates from a genuine optimum power, because the previously stored correlation characteristic between the first and second layers has changed.
In order to cope with this problem, it is necessary to perform the OPC by shifting a recording power changing range for tentative writing (that is, the OPC should be retried), which results in extra consumption of time required for adjustment and excessive use of the PCA.
In addition, in general, the second layer is lower than the first layer in the sensitivity (the magnitude of change) of the asymmetry value β to the recording power. This fact means that when the asymmetry value-to-recording power characteristic changes with variations of temperature or the like, the second layer will exceed the first layer in the amount of the recording power which should be changed in order to maintain the optimum asymmetry value.
Therefore, in a case that the OPC is performed by changing the recording power within a predetermined search width, centering on a recommended recoding power, such a situation may occur that even though, in the first layer, the optimum asymmetry value can be obtained within the predetermined retrieval width, centering on a recommended recording power for the first layer, in the second layer, no optimum asymmetry value can be obtained within the same search width, centering on a recommended recording power for the second layer.
Also, in this case, the retrieval range should be shifted to retry the OPC, which results in an increase in time required for adjustment and excessive use of the PCA.
In a write-once type optical disc, even though some recording area for normal data still remains unused, when the predetermined PCA is used up, it will become impossible to newly record data on the optical disc concerned at that moment. For this reason, the excessive use of the PCA should be avoided as much as possible.